Becoming a marine mammal trainer is one of the jobs in the animal field, that is highly competitive to get. There are much more applicants for the jobs, than there is job openings. It is a a lot of hard work to get a job in this field, and requires a lot of dedication to accomplish it. If you are still interested in pursuing this career, continue reading.
Most marine mammals that you see in zoos or aquariums are seals, sea lions, sea otters, walruses, dolphins, beluga whales, and even killer whales(the largest member of the dolphin family). As a trainer your duties consist of prepping food (lots of fish!) and feeding the animals. You also are responsible for the cleaning and care of the exhibit the animal is in. You will spend a good amount of time, training the animals in your care. Training is mostly for husbandry purposes. This helps the veterinarian staff monitor the animals health. For example, a trainer may train a seal to present a flipper for a blood draw, or a bottlenose dolphin will turn over and present its underside to receive an ultrasound. Some facilities have educational presentations that they also train animals for. This is a way to connect the audience with the animals, and make people more appreciative of the different animals species. Connecting with people is a good way to raise awareness of issues facing these amazing animals in the oceans and environments they live in.
As far as education requirements go, you need a high school diploma. Since competition is very strong, having a degree would be very helpful. Some common degrees among trainers are in biology, zoology, psychology, and even animal behavior. As with most zoological or aquarium facilities, I recommend getting prior animal experience. Volunteering at a zoo or aquarium is helpful. If that is not possible, working or volunteering your time at a stable, veterinarian clinic, or animal shelter will help get you some hands on experience.
Most marine mammal training positions require being scuba certified and completing a swim test, before you are considered to be hired. Being in good physical shape is required of these jobs. Keeping a healthy diet and exercise is very beneficial for you in this line of work. Another quality you have to be comfortable with, is public speaking. If you are not comfortable talking to groups of people, or talking during a presentation, this will not be the job for you.
However, even after seeing the requirements and knowing that it is a very competitive field, and you still think this is the field for you; I offer one more bit of advice. Stay persistent and do not be discouraged if you do not get the first couple of jobs your apply for.